experimental studies of magnetically scannable leaky wave antennas having corrugated ferrite slab...

7/30/2019 Experimental Studies of Magnetically Scannable Leaky Wave Antennas Having Corrugated Ferrite Slab Dielectric L

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IEEE TRANSACTIONS ON ANTENNAS A ND PROPAGATION. VOL. 36, NO. 7, JU LY 1988 911

Experimental Studiesof Magnetically ScannableLeaky-Wave Antennas Having a CorrugatedFerrite Slab/Dielectric Layer Structure

Abstract-The radiation characteristics of a magnetically scannableleaky-wave antenna using a corrugated ferr ite slab support by a T eflonwaveguide have been demonstrated experimentally. A corrugatedpolycrystalline yttrium ir on garnet (Y IG) slab having the dimensions150.0 x 15.0 x 1.0 mm3 has been fabricated. T he corrugation depth,corrugation spacing, and number of corrugations are 150.0 pm, 2.0 mm,and 55.0, respectively. E xperiments have been carri ed out in themill imeter wave frequency range fr om40.0to 50.0GHz. The main beamdirection of the leaky wave shifts continuously about 41.0' at theoperating fr equency 46.8 GH z by altering the dc magnetic field up to 1.4T . It is found that the corresponding half-power beamwidth varies from3.2" t o 3.6" and a maximum scanning rate is 1.0'/0.02 T . Experimentalresults are compared with theory based on the dispersion relation of theferr ite slab/dielectric layer structure.

I . INTRODUCTIONEAKY-wave phenomena in corrugated slab waveguidesL re very attractive subjects for applications to millimeterwave antennas for high-resolution radar [11. The leaky-waveantenna using the inverted strip dielectric waveguide has beensimulated by a small mechanical motion to change an air gapbetween two quasi-planar dielectric slabs. The response ofsuch a mechanical scanning antenna mght be too slow formany applications [2]. The electronically scannable leakywave antenna using silicon waveguide with metallic gratingshas been studied by Horn, Jacobs, Freibergs, and Klohn toachieve a high-speed scanning behavior [3 , [4]. However, theline scanning is not continuous as a function of modulating

current of the distributed p-i-n diodes. The radiation ofmllimeter wave from a corrugated ferrite image line has beenproposed and demonstrated experimentally by Ohira et al. [5].This paper reports experimental studies on a magneticallyscannable eaky wave antenna with one corrugated ferrite slab,proposed by Ohira et al., in an insulated image guideconfiguration which exhibits potentially a more practicaldesign for millimeter wave integrated circuits.11. THEORETICALORMULATION

The geometry of the structure under study is shown in Fig.1.A corrugated ferrite slab having the permeability tensor f i issupported by a dielectric slab with relative permittivity frd ,which is backed by a conductive plane and is magnetized in the

Manuscript received October 10, 1986; revised April 17, 1987. This workwas supported in part by the Murata Science Foundation.The authors are with the Faculty of Engineering, Osaka University,Yomada-Oka, 2-1, Suita 565, Osaka, Japan.IEEE L og Number 8820222.

zdirection. The thickness of the ferrite slab and dielectric slabaret andh, respectively. In the structure of Fig. 1,most of theelectromagnetic energy will be concentrated within the corru-gated ferrite slab due to the high permittivity f r f . Theconduction losses in the structure mght be decreased byseparating the ferrite slab from the metal plate by a dielectricslab [2].In the theory, we assume that the effect of the corrugationon the ferrite slabis neglected due to the small perturbation ofthe surface and that the fundamental space harmonic00of theleaky-wave phenomena is close to the propagation constantPof the guided wave [11. The permeability tensor of the ferriteslab is given by

f i = [ j K K 0]where

and

y, M and HO are the gyromagnetic ratio, the saturationmagnetization, and the dc magnetic field, respectively [6].We assume that the structure is uniform and infinite inextent in the dc magnetic field direction (zdirection). Sincethe transverse electric (TE) mode exhibits a sensitivity to thedc magnetic field for the two-dimensional structure of Fig. 1,we will treat this mode with field componentsH ,, Hy,andE,[6]. From Maxwell's equations, theE, components satisfy thefollowing differential equation:

0018-926X/88/0700-0911$01OO O 1988 IEEE


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912 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION. V OL 36. VO 7 . CL Y 1Y88

Fig. 1. Geometry of corrugated ferrite slab/dielectric layer structure

wherep,ff = ( p 2 - ~ ) / pnd they dependence of the fields isassumed to be exp (-jP y ) with propagation constant P .Equation (2) can be easily solved for E , in each regionE a -G . e - axo ( x - w ) , t


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S f A H E K I ei U / . MAGNET I CALLY SCANNAK1.E LEAK Y -WAV E ANTENNAS

Fig. 4. Photograph of corrugated ferrite slahidielectric laker \tructureThe upper surfaceof the slab was corrugated with rectangulargrooves. The width, depth. corrugation spacing and thenumber of corrugation were 1 O mm, 7 = 150.0pm, d = 2.0mn. and N = 55, respectively. The lower surface of thesample was supported by a Teflon slab having the dielectricconstant t,d = 2.1, which was bonded to a copper plate byusing wax as shown in Fig. 1. The dimensions of the Teflonslab were thicknessh = 3.4 mni. width wd = 11.65 mm, andlength L = 150.0 mm.Fig. 5depicts the measurement setup. The millimeter wavewas generated by an IMPATT oscillator sweeping in thefrequency range 40.0-50.0 GHz and was fed through arectangular WRI-500 waveguide providing TE,, mode. Toexcite the TE mode in the layered ferrite structure, the ferriteslab was held parallel to the electric field of the TElomode. Toenhance the launching efficiency, the slabs had a taperedtransition section at the front end. The far ends of the slabswere also tapered and coated with carbon absorber to avoidunwanted reflections. The slab was inserted into an electro-magnet having large magnet poles of dimensions 15O x 15 Ocm2. The leaky wave signal was detected through a standardhorn at a distance of 106.5 cm from the center of thecorrugated ferrite slab.Figs. 6 and 7 show the experimental results for the mainbeam direction as a function of dc magnetic field for twodifferent operating frequencies 46.8 and 50.0 GHz. At thezero magnetic field in Fig. 6, the direction of the main beamB,,, was measured to be O n r ~ )= +0.5" toward the endfiredirection from the broadside. By increasing the dc magneticfield a continuous scanning of the main beam up to Omax =-40.5" was observed. We can estimate from Fig. 6 that theslope or scanning rate, A8,,/Ap&o increases rapidly as thegyromagnetic resonance field, poHK l 1.4T is approached.The maximum range of scanning 1 B,,,,, 1 + B,,,o is 41', whichcorresponds to an average scanning rate of 1"/0.034 T.Similar scanning characteristics of the main beam wereobserved at the frequency 50.0 GHz, as shown in Fig. 7.Thee,,, is +16" and the average scanning rate is found to be 1"/0.036T.The main beam direction, O m , of the leaky wave antenna isgiven approximately by [ I ]O,,,=sin-' [(&+2n7r/d)/ko], n=O, - t l , +2, . .. (6)

Fig. 5 . Photograph of experiinental setup for mea\urernents of radiationbcain under dc niagnetic field

wheren is the numhcr of thc space harmonic. For t i = ~ 1 , /3,,becomes complex. We assume the corrugation depth v issufficiently small that the imaginary part of P o mght beneglected and its real part corresponds to the propagationconstant p of the guided wave in Figs. 2and 3.Expression (6)was evaluated numerically by estimating the propagationconstant /3 of dispersion relation (5) as a function of dcmagnetic field, and the results are shown in Figs. 6and 7 withsolid lines. In the calculations the actual thickness of the ferriteslab has been regarded as t = 850pm. taking into account thecorrugation depth 17 of 150.0pi .The experimental data in the main beam direction agree wellwith the theoretical prediction. Figs. 8 and 9 show theexperimental results for the half-power beamwidth O ,, and theamplitudeA of the main beam as a function of the dc magneticfield for two different frequencies. At the operating frequency.46.8 GHz, of Fig. 8, the amplitude of the main beam seems tobe increased with increasing magnetic field but decreasesabruptly in the vicinity of the gyromagnetic resonance field,


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e m-2 0

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 36, NO . I , UL Y 1988

- f = 50.0 GHz

- 4 0 1 I'

5 + 2 02

I= 46. 8GHz: EXPERIMENT- THEORY

-

+100.0 05 1.0 1 5 CT

sin (NQ/2)N sin (Q/2)(8)=

DC MAGNETIC FIELD PoHoFig. 6. Measured and calculated variation of main beam direction asfunction of magnetic field at 46.8 GHz.

2

E 5i:. .. ...%I

'oHR1 1I I I01) 0.5 10 15 C

-mW3>W

a2c4n-WO32-f

D C MAGNETIC FIELD Po HFig. 8. Ampli tude and beamwidth of main beam versus dc magnetic f ield at46.8 GHz.

Expression (7) is evaluated numerically with the materialparameters used in the experiments and is shown inFigs. 8and9 with solid lines. I t can be seen in the figures that thetheoretical curves agree well with the experimental data.Figs. 10 and 11 show the experimental results for typicalradiation patterns for different magnetic fields at the operatingfrequencyf = 46.8 GHz. It can be seen in Fig. 10that themain beam direction8 is - 15.5", he first sidelobes are 19-21 dB below the level of the main beam, and the half-powerbeamwidth 8, is about 3.4". In the vicinity of the gyromag-netic resonance field of Fig. 11, the main beam direction8 is-34" , and the radiation pattern seems to be distorted andbroadened, with a half-power beamwidth8, = 6.5".The theoretical radiation pattern is approximately given byU1

0. 0 0.5 10 15 I ID C MAGNETIC FIELD Po H

Fig. 7. Measured and calculated variation of main beam direction asfunction of magnetic field at 50.0GHz.

poH ~1= 1.4T. On the other hand, in Fig. 9, the amplitudedoes not depend strongly on the dc magnetic field. In thefigures, the abrupt change in the amplitude of the main beamnear the gyromagnetic resonance field causes the largescanning rate.The dependence of beamwidth8 on the magnetic field isalso shown in Figs. 8and 9. It is found in these figures thatbeamwidths first decrease slightly with increasing the dcmagnetic field, but in the vicinity of the gyromagneticresonance field the beamwidth increases very rapidly. Theaverage values of beamwidth below magnetic field intensity1.3 T may be evaluated as3.5" at46.8 GHz and 3.2" at 50.0GHz.A theoretical expression for the beamwidth is given by [l ]

e,=2 [sin-1 (2) sic1 (-+-)I-39h P n (7)Nr d kowhere X, = 2r/ko, 0 = Po - 2r/d, and n = - 1.

where $ = (kod sin 8 - P,d). The expression (8) wasevaluated numerically by using the P value in Fig. 3and isdepicted with solid lines in Figs. 10and 11. The computeddata in Fig. 10 exhibit that the main beam direction 8 is- 6" , and the half-power beamwidth is 8, = 3.0" in goodagreement with the experimental results. However, in theexperimental data the first sidelobe cannot be separated clearlynear 8 = - 0" . In Fig. 11a large discrepancy between thetheoretical and experimental radiation patterns appears in therange of 8= -30to - 0" .This discrepancy may be causedby the sensitivity of the propagation constant near thegyromagnetic resonance field as shown in Fig. 3. Further-more, the loss effect of the ferrite material will be significantnear the gyromagnetic resonance field.It is well known that the direction of the main beam8 is afunction of the operating frequency [l]. 0, was measured bychanging the frequencies for various magnetic fields (0.0-1.3T). The results are shown inFig. 12. The negative sign of the8 on the abscissa of the figure denotes the scanning of themain beam toward the backfire region, and a positive sign


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MAHERI et al.: MAGNETICALLY SCANNABLE LEAKY -WAVE ANTENNAS

-n

-

915

wE20

rn3I

- 1521W

z- 10g-

W3- 5 53P

VIg20-sI

15-35

GHzEXPERIMENTTHEORYEXPERIMENT

n - 1

0. 0 0. 5 10 1 5 C T ID C MAGNETIC FIELD Po H

Fig. 9. Amplitude and beamwidth of main beam versus dc magnetic field at50.0 GHz.0m- 5U

-10

-1 5

-2 0

- 250 (DEGREES)

Fig. 10 . Comparison of experimental and theoretical data of radiationpatterns at dc magnetic field of 1.23 T.

- 50 - 4 0 - 30 - 209 (DEGREES)Fig. 11. Experimental and theoretical data of rad ati on panern near gyro-magnetic resonance field of 1.43 T.

+20L ' ' ' ' '40 42 44 46 40 50 GHzF REQUENCYFig. 12 . Variation of main beam direction 0, versus frequency for dcmagnetic field as parameter.

indicates scanning toward the endfire region. It can be seenthat the change in the sign of 8 occurs at high frequencies forlower magnetic fields and always above 46.0 GHz. Plottedpoints for the experiments agree well with computed valuesshown with solid lines for a wide range of the operatingfrequencies40.0-50.0 GHz.The measured radiation pattern in the H-plane is shown inFig. 13 along with the measured values in the E-plane. Weobtain an H-plane half-power beamwidth Ow of 12" and abeamwidth of 35O below 20dB, which is about the same half-power beamwidth provided by Trinh et al. for a specialarrangement designed to reduce the beamwidth in the H-plane[7]. However, they achieved a beamwidth of about 46" at-20dB. Thus, our results seem narrower than theirs.The main beam peaks in theE-and H-planes inFig. 13areseparated slightly. This may be due to the complexity of thethree-dimensional measurements in the H-plane.Next we examined the effect of the air gap between themagnet poles on radiation pattern, because the sample is put inthe center of large magnet poles. The measurement wascarried out at the operating frequency 46.8 GHz and at aconstant magnetic field 0.66 T while changing the air gap ofthe magnet poles to 18.0, 36.0, and 56.5 111111 The measuredradiation patterns are shown in Fig. 14. It can be seen that themain beam direction8 is independent of the air gap but thatthe beamwidth can be reduced by decreasing the air gap.Concerning the effect of the width of the dielectric slabw ,,radiation patterns were measured by changingw , from 11.65to 3.4 mm. It was found that the beamwidth, e wasdecreased about 18.0percent by reducing the width of slab,but the sidelobe levels rose by 7 dB compared with 14 dB inthe wide Teflon slab case.Finally, we examined the effect of the corrugations. Aferrite slab without corrugation was supported by a corrugatedTeflon slab with the structure of Fig. 1.Measurements werecarried out in a dc magnetic field of 1.23 T at the operatingfrequency 46.8 GHz. The direction of the main beam8 was


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AIR GAP i2\. I =46.8GHz--: le rnm f; p--:36rnm i l c i

! :.....>I ! ( l .Ili: I !I! P0H0=0.66T

2 j -..,, ? ,A\ / I ! i!w : ;,i\;4 /.\ ;

I ;i !i\ !-20 - \\I\ ! i !

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...

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATI ON, VOL. 36. NO . 7, UL Y 1988

cally from the dispersion relation of the TE wave. ApolycrystallineYIG slab having dimensions 150.0x 15.0 x1Om3as been used, where the depth, corrugation spacing,and number of corrugation are 150.0 pm, 2.0 mm, and 55.0,respectively. Themain beam direction, the beamwidth, and theradiation pattern of the leaky wave have been measured as afunction of dc magnetic field in the frequency range 40.0-50.0GHz. It is shown that the main beam direction can be steeredcontinuously by altering the bias magnetic field and stronglydepends on the bias magnetic field near the gyromagneticresonance. The maximum scanning angle of the main beamdirection is seen to be 41.0 associated with an averagebeamwidth of 3.4with the bias magnetic field up to 1.4 T at46.8GHz.The maximum scanning rate is found tobe 1l0.02T. Measured results agree well with computed data based on

e (DEGREES)Fig. 13. E- and H-plane radiation patterns of magnetically scannable leakywave antenna for 1.23 T.

noted at - 5.5 for poHo= 1.23 T, which is the same value [11as the corrugated ferrite slab. The half-power beamwidth 8 ,was measured to be about 2.4, indicating a narrower r2]beamwidth than that for the corrugated ferrite slab, but theradiated power was about 16 dB smaller than in the corrugatedferrite slab case. The weak signal is due principally to the lowpermittivity,d of the dielectric slab. In other words, sincemost of the electromagnetic energy concentrates in the high-permttivity ferrite slab, the effect of the corrugation on thedielectric slab may not contribute much to an efficient

r31[4]

radiation of the leaky wave. r51IV . CONCLUSIONThe magnetically scannable leaky wave antenna employinga corrugated ferrite slab supported by a Teflon slab has beendemonstrated experimentally in the millimeter wave frequencyrange. Assumng that the corrugation depth is sufficiently

[61

[71

REFERENCESP. Bhartia and I. J . Bahl, Mil limeter Wave Engineering andApplications.T. I toh andA. S . Hebert, Simulation study of electronically scannableantennas and tuneable filters integrated in a quasi-planar dielectricwaveguide, IE EE Trans. M icrowave Theory Tech., vol. MTT-26,pp. 987-991, Dec. 1978.K . L . Klohn, R. E. Horn, H. Jacobs, and E. F reibergs, Siliconwaveguide frequency scanning linear array antenna, IEEE Trans.Microwave Theory Tech.,vol. MTT -26, pp. 764-773, Oct. 1978.R. E . Horn, H. J acobs, E. Freibergs, and K. L . K lohn, Electronicmodulated beam steerable silicon waveguide array antenna, IEEETrans. Microwave Theory Tech., vol. MTT -28, pp. 647-653, J une1980.T. Ohira, M. Tsutsumi, and N. Kumagai, Radiation of mill imeterwaves from a grooved ferrite image line, Proc. IEEE (L etter), vol.70, pp. 682-683, J une 1982.T. J . Gerson and J . S . Nadan, Surface electromagnetic modes of aferrite slab, IEE E Trans. M icrowave Theory Tech., vol. MIT-22,T. N. Tri nh, R. M ittra, and R. J . Paleta, Horn image guide leaky-wave antenna, in Tech. Dig. I 981 IEEE I nt. Microwave Symp., pp.20-22.

New Y ork: Wiley, 1984, pp. 307-598.

pp. 151-763, A ug. 1974.


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MAHERl et al. : MAGNETICALLY SCANNABLE LEAKY-WAVE ANTENNAS 91 7Heshmatollah Maheri was born in Kerman, Iran,on Apri l 21, 1947. He received the DipLIng. degreein communication engineering from the TechnicalUniversity of Aachen, Federal Republic of Ger-many, in 1976, and the Ph.D . degree in communi-cation engineering from Osaka University, Osaka,J apan, in 1987.From 1976 to 1983 he was a Lecturer in theDepartment of El ectrical Engineering at the Techni-cal Col lege of K erman, the University of Guilan andthe Kerman University, in I ran. He also served asHead of the Electrical Engineering Department in the Technical Col lege ofKerman and the University of Guilan. He is currently attached to theResearch L aboratory of the Antennas and Satelli te Communication Depart-ment of M itsubishi E lectric Corporation, in Osaka, Japan. His presentresearch interests are mainly in microwave and millimeter-wave antennas andassociated measurement techniques.Dr. Maheri is a member of the Institute of El ectronics, Information andCommunication Engineers of Japan. He was awarded a Mombusho Scholar-ship by the Japanese Government in 1984.

M akoto Tsutsumi (M 71) was born in Tokyo,J apan, on February 25, 1937. He received the B.S.degree in electrical engineering from RitsumeikanUniversity, Kyoto, in 1961, and the M .S. and Ph.D .degree in communication engineering from OsakaUniversity, Osaka, Japan, in 1963 and 1971,respectively.From 1974 to 1983, he was a Lecturer, and since1984 he has been an Associate Professor of Com-munication Engineering at Osaka University. F romMay to November 1987 he was a Visiting ResearchFellow at University of Wales Institute of Science and Technology, Cardiff ,UK . H is research interests are primaril y in microwave and millimeter-waveferrite devices. He has published 80technical papers on these topics in variousjournals

Dr. Tsutsumi is a member of the Institute of El ectronics, Information andCommunication Engineers of J apan and the Japan Society of Applied Physics.

Nobuaki K umagai (M59-SM71-F81) was bornin J apan on May 19, 1929. He received the B.Eng.and D.Eng. degrees from Osaka University, Osaka,J apan, in 1953 and 1959, respectively.From 1956 to 1960, he was a Research Associatein the Department of Communication Engineeringat Osaka University. From 1958 through 1960, hewas a Visiting Senior Research Fellow at theElectronics Research Laboratory of the Universityof California, Berkeley, while on leave of absencefromOsakaUniversity. F rom 1960 to 1970, he wasan Associate Professor of Communication Engineering at Osaka Universityand became a Professor in 1971. From 1980 to 1982, he served as Dean ofStudents of OsakaUniversity. In A pril 1985 he became Dean of Engineeringof OsakaUniversity, and he has been a President of Osaka University sinceAugust 1985. His fields of interest are electromagnetic wave theory and i tsapplications to the microwaves, mill imeter-waves, and acoustic-waves engi-neering, optical f ibers, integrated optics, and related optical wave techniques,and laser application engineering. He has published more than 100 technicalpapers on these topics in established ournals. He is the author orcoauthor ofseveral books.Dr. K umagai is a member of the Instituteof Electronics, Information andCommunication Engineers (IEI CE ), the Institute of E lectrical Engineers ofJapan, and of the Laser Society of Japan. He has received the AchievementAward from the Instituteof Electronics and Communication Engineers ofJapan and the Distinguished Services Award from the IE ICE , and the SpecialAchievement Award fromLaserSociety of J apan. From 1979 to 1981, he wasChairman of the technical groupon M icrowave Theory and Techniques of theInstituteof Electronics and Communication Engineers of J apan, and was V icePresident of the IEI CE in 1980-1982. He is a member of the Telecommunica-tions Technology Council of the Ministry of Post and Telecommunicationsand the Broadcasting Technology Council of J apan Broadcasting Corporation(NHK) and is a Consultant for the Nippon Telegraph and TelephoneCorporation(IT).

experimental studies of magnetically scannable leaky wave antennas having corrugated ferrite slab...

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